This relates generally to imaging systems and, more particularly, to complementary metal-oxide semiconductor (CMOS) image sensors with global shutter functionality.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imager sensors (sometimes referred to as imagers) may be formed from a two-dimensional array of image sensing pixels. Each pixel includes a photosensitive layer that receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format.
Image sensors can operate using a global shutter or a rolling shutter scheme. In a global shutter, every pixel in the image sensor may simultaneously capture an image, whereas in a rolling shutter each row of pixels may sequentially capture an image. In order to implement a global shutter, image sensors may include one or more charge storage regions coupled to a floating diffusion region in each pixel. Two source follower transistors are sometimes used to implement global shutter functionality in conventional imaging pixels. However, including two source follower transistors in each imaging pixel may take up large amounts of pixel area.
It would therefore be desirable to provide improved global shutter pixels for image sensors.